The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions.
With the rapid increasing of IP network data services, operators have an increasing demand for transmission capacity. The capacity of a single fiber in an existing network is gradually approximating to the limit of 100 Tbps. Although commercial 100G transmission systems have already been available, how to further increase the transmission capacity on the basis of 100G transmission signals has drawn the attention of equipment manufacturers and operators.
A PM-QPSK modulation technology, a coherent detection technology and a DSP processing technology adapted in systems of 100 G decrease an optical signal-to-noise ratio (OSNR) margin of the systems to an order of magnitude equal to 10 G, and lower a requirement of the systems on optical fibers. Researches show that transmission can be performed over a distance greater than 1000 km in the 100 G systems by using ordinary G.652.D optical fibers or low loss and ultra low loss optical fibers. By using ultralow loss optical fibers, link distances can be extended by 35-40%, and the number of transmission stations can be decreased on some lines, thereby facilitating construction of all-optical networks. In addition, in certain systems having an optical amplifier span of a long distance around 100 km, ULL optical fibers can effectively reduce cross-span loss.
Because a limited OSNR, noise, and nonlinear problems are generated in transmission systems of 400 G, a transmission distance is limited. According to current test results of mainstream device providers, a transmission distance of systems of 400 G using dual-carrier and a modulation technology of 16QAM is only around ⅓ of that of systems of 100 G. Therefore, requirements on a system capacity and a transmission distance need to be comprehensively considered in construction of high-rate systems. From the perspective of line-side transmission devices, a multicarrier light source, higher order modulation, coherent detection, a high-speed DSP system, an error correction technology, and the like may be used to promote development of commercialized high-speed optical transmission systems. From the perspective of a link optical fiber technology, ultralow-loss optical fibers can improve a system OSNR and effectively extend a transmission distance.
Currently, attenuation of a conventional G.652.D optical fiber is generally 0.20 dB/km, and optical energy gradually decreases after being transmitted at a long distance. Therefore, a signal needs to be amplified again by means of relay. Compared with costs of optical fiber cables, related devices and maintenance costs of transmission stations account for above 70% of an entire link system. Therefore, an ultra low attenuation optical fiber can effectively extend a transmission distance, and reduce construction and maintenance costs. According to related calculation, if optical fiber attenuation decreases from 0.20 dB/km to 0.16 dB/km, construction costs of an entire link decrease by around 30%. In conclusion, development, design, and production of an ultralow attenuation optical fiber become an important subject in the field of optical fiber production.
Chinese Patent Application No. 201310394404 discloses a design of an ultra low attenuation optical fiber. Outer cladding layer of pure silicon dioxide is used in the ultra low attenuation optical fiber. However, because a typical step cross-section structure is used in the ultra low attenuation optical fiber, an optical fiber bending is not optimized by using a trench cladding layer design. In addition, a core layer of the ultralow attenuation optical fiber is not doped with Ge, and consequently, viscosity mismatch may occur when a preform is prepared. In addition, attenuation and bending ability thereof are relatively poor.
U.S. Patent Publication No. 2010/022533 discloses a design of pure-silicon core to obtain a smaller Rayleigh coefficient. Germanium and fluorine are not both doped in a core layer, and fluorine-doped silicon dioxide is used as an outer cladding layer in the design of pure-silicon core. In the design of pure-silicon core, complex viscosity match needs to be performed inside an optical fiber, and an extremely low speed is required in a belt grinding process, to avoid an attenuation increase caused because high-speed belt grinding results in a defect inside the optical fiber. Accordingly, a production process is very complex.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.